1. Technical Field
The present invention relates to food products. More particularly, the present invention relates to methods for treating fats and oils especially fish oils and dairy fats and oils, for deodorization and/or cholesterol level reduction. In its product aspect, the present invention relates to edible fats and oils, especially fish oils and dairy fats and oils, characterized in part by bland flavor and reduced cholesterol level.
2. Background Art
A great deal of attention has been given to the various health benefits apparently associated with the consumption of fatty fish. The health benefits appear to be related to the presence of high levels of the n-3 family of polyunsaturated fatty acids. Oils containing these fatty acids, such as fish oils, are referred to as "omega-3" oils and desirably contain high levels of n-3 fatty acids, especially eicosapentaenoic acid ("EPA") and docosahexaenoic acid ("DHA").
Notwithstanding the present interest, non hydrogenated fish oil, generally, to date has not been used widely in food products due to problems in odor, flavor and especially stability, primarily oxidative rancidity. Also, fish oil undesirably contains cholesterol. However, canned salmon has had added salmon oil. Also, certain canned meat products have been marketed in Japan which have had refined fish oil added as a nutritional supplement.
Hydrogenated fish oils are much more stable due to the decrease in the degree of polyunsaturation and are widely used in Europe for margarine. Hydrogenation is also effective in reducing odor and off-flavor development after deodorization. However, hydrogenation by decreasing polyunsaturation, including the n-3 fatty acid content, correspondingly decreases the health value of fish oil.
The present invention in its broad aspect relates to a physical method for reducing the cholesterol level of, and/or deodorizing fats and oils. For fish oil in which high levels of undesirable odor and cholestrol, are problems, the present invention involves the simultaneous reduction of cholesterol level and deordorization. For dairy and various other fats and oils which have high native cholestrol levels, but which do not have particular other problems, the focus of the present invention is directed principally to the reduction in cholestrol level, even though deordorization may also occur. Reducing the cholesterol content of a fat or oil is also nutritionally important since reducing cholesterol intake can reduce serum cholesterol, and reducing serum cholesterol has been shown to lower the risk of heart disease. Chemical extractant methods for cholesterol removal or reduction in oils are known. Chemical methods are too expensive, however, for commercial scale use. Also, chemical extraction undesirably results in the production of oils contaminated by residual amounts of chemical extractants. While several chemical methods for removing cholesterol are known, the only physical method believed known in the art is molecular distillation.
Molecular distillation for cholesterol reduction, however, requires extreme operating conditions including a pressure in the micron range. While molecular distillation is effective for removing some but not all cholesterol, the process can yield a fish oil with undesirable darkening of oil color and an undesirable strong "chemical" flavor. The dark color and off-flavor are due to the presence of odoriferous materials which remain after completion of molecular distillation. Thus, with respect to fish oils, molecular distillation still requires subsequent deodorization. The two processes cannot be combined since the vacuum conditions which define molecular distillation preclude the addition of steam which strips off these odoriferous materials. Additionally, commercial scale molecular distillation equipment is very costly. Most importantly from a cost standpoint, another major disadvantage of molecular distillation is the significant product loss which is associated with the "distillate" fraction. In molecular distillation the distillate fraction can run from 7% to as high as 20% or higher in order to achieve cholesterol reduction comparable to the results of the present invention. Since the distillate fraction is unusable due to its containing the undesirable constituents in concentrated form, such high distillate fractions reduce overall yields. Reduced yields is a most significant cost factor due to the high cost of the starting material in addition to the high cost of molecular distillation itself.
In accordance with the present invention, another physical method has been discovered for removing substantially all of the free or "non-esterified" cholesterol from fats and oils whereby the overall cholesterol level is reduced and many of the disadvantages of molecular distillation are overcome. In the principal operative step of the present invention, the operating conditions utilize a much higher pressure than employed in molecular distillation, so as to maintain steam during stripping. Surprisingly, these conditions are nonetheless effective for cholesterol removal. Furthermore, the equipment needed to practice the method is commercially available on a commercial scale, is less expensive compared to molecular distillation equipment, and is much less expensive to operate. More importantly, the distillate fraction is as low as 1% compared to the 20% for molecular distillation.
Deodorization of oils by steam stripping is commonly the finishing step in edible oil processing, including those processes involving molecular distillation such as to reduce cholesterol. The typical equipment employed contains set stations which sparge steam into a body of oil with high baffeling. Conventional deodorization can remove some sterol materials, but such reduction is very modest. In addition to reducing cholesterol level, another surprising benefit of the present invention that the present process deodorizes the fish oil simultaneously with cholesterol level reduction without substantial destruction of desirable n-3 fatty acids. Thus, a further surprising advantage of the present invention is that the conventional oil finishing deodorization step is made optional rather than mandatory for the realization of clean fish oils. In certain embodiments of the present invention a deodorization step may still be desirable, such as when cleaned fish oils of highest possible purity and quality are desired.